The influence of changing the position of the feedwater sparger on the thermal-hydraulic stabilit... more The influence of changing the position of the feedwater sparger on the thermal-hydraulic stability of natural-circulation boiling water reactors (BWRs) is investigated. Frequency-domain, linear stability analysis is applied using a reduced-order dynamic model. It is found that the phase with which the temperature oscillations, created at the feedwater sparger, reach the core inlet has a significant influence on the stability.
A relatively simple subchannel void-fraction measurement system was developed and applied to a sc... more A relatively simple subchannel void-fraction measurement system was developed and applied to a scaled model of a BWR fuel assembly. The measurement system is based upon the gamma-transmission technique and uses a tomographic reconstruction procedure to calculate the void-fractions in the subchannels. Data pre-processing is used to remove positioning errors of the gamma source and detector. Measurements are performed under dierent operating conditions and radial power pro®les. The measurements are compared with the drift-¯ux two-phase¯ow model. The void-fraction in the wall and corner subchannels is lower than average. By applying the drift-¯ux model to each subchannel separately and comparing this calculation with measurements the presence of lateral void-drift should be detectable. However, the data do not show evidence for lateral void-drift. By comparing two chordal void-fractions, one through the fuel rods and one in between the fuel rods, a¯ow pattern transition could clearly be seen between a void-fraction of 30% and 40%. 7
Investigations on Type-I (hydrostatic head) and Type-II (density wave) BWR stability characterist... more Investigations on Type-I (hydrostatic head) and Type-II (density wave) BWR stability characteristics are reported. Experimental data are obtained from the Dodewaard natural-circulation BWR at conditions far away from nominal operating points. The Type-I stability boundary was reached; the Type-II stability boundary was crossed. At this latter unstable condition the reactor power showed peculiar oscillation modulations. Experimentally obtained decay ratios and resonance frequencies are put into context using a physical model. Flashing is shown to be an important phenomenon for driving the coolant flow at start-up conditions and for Type-I stability features. From low-pressure experiments, it appears that the decay ratio is an unsafe measure for Type-II stability close to the stability boundary.
ABSTRACT The evaluation of experimental techniques for the determination of the subcriticality le... more ABSTRACT The evaluation of experimental techniques for the determination of the subcriticality level of an ADS core relies on reactor point kinetics. The measured parameters depend on the detector position, and the reactivity values are subject to spatial correction factors (SCFs). In this paper the contribution of different eigenmodes to the SCF for the pulsed neutron source (PNS) technique is assessed. Moreover by pulse simulations, precise values of the correction factor are obtained. As case study, the VENUS-F SC1 subcritical core is investigated, with a pulsed neutron source in the center of the core, generated by the GENEPI-3C deuteron accelerator. Much more than 100 modes need to be taken into account to precisely obtain the spatial correction factor for the area method evaluation of this core. Especially the modes with a maximum in the center of the core contribute significantly to the SCF. No spatial correction needs to be applied close to the zeros of the first mode with a maximum in the center of the core (different from the fundamental one). In the reflector zone, the absolute reactivity level is overestimated.
The influence of changing the position of the feedwater sparger on the thermal-hydraulic stabilit... more The influence of changing the position of the feedwater sparger on the thermal-hydraulic stability of natural-circulation boiling water reactors (BWRs) is investigated. Frequency-domain, linear stability analysis is applied using a reduced-order dynamic model. It is found that the phase with which the temperature oscillations, created at the feedwater sparger, reach the core inlet has a significant influence on the stability.
From the beginning of BWR technology it was realized that a BWR can become unstable under particu... more From the beginning of BWR technology it was realized that a BWR can become unstable under particular circumstances caused by a feedback between the thermal-hydraulics and the neutronics. This instability can result in oscillations of the power and the flow rate, which is an unwanted phenomenon.The NACUSP project addresses the stability issues in current and future BWRs by expanding the
By altering the coolant flow direction in a pebble bed reactor from axial to radial, the pressure... more By altering the coolant flow direction in a pebble bed reactor from axial to radial, the pressure drop can be reduced tremendously. In this case the coolant flows from the outer reflector through the pebble bed and finally to flow paths in the inner reflector. As a consequence, the fuel temperatures are elevated due to the reduced heat transfer of the coolant. However, the power profile and pebble size in a radially cooled pebble bed reactor can be optimized to achieve lower fuel temperatures than current axially cooled designs, while the low pressure drop can be maintained.
... et al., 2003 WJM De Kruijf, KCJ Ketelaar, G. Avakian, P. Gubernatis, D. Caruge, A. Manera, TH... more ... et al., 2003 WJM De Kruijf, KCJ Ketelaar, G. Avakian, P. Gubernatis, D. Caruge, A. Manera, THJJvan der Hagen, G. Yadigaroglu, G. Dominicus, U. Rohde, H.-M ... Zboray et al., 1999 Zboray, R., Manera, A., De Kruijf, WJM, van der Hagen, THJJ, van Bragt, DDB, van Dam, H., 1999. ...
The use of the decay ratio as a practical stability measure of boiling water reactors is question... more The use of the decay ratio as a practical stability measure of boiling water reactors is questioned. Especially, it is shown that a reactor working at an operating point with a small decay ratio can be closer to instability than a reactor with a larger decay ratio. Consequently, a reconsideration of the practical use of the decay ratio is advocated. :c~
Usually, heat transfer from fuel to coolant is treated as a first-order process in reduced-order ... more Usually, heat transfer from fuel to coolant is treated as a first-order process in reduced-order boiling water reactor dynamic models. The correctness of this simple approach is investigated by comparing reactor stability predictions of the March-Leuba reduced-order model, with those using a second-order model. The predicted margin to instability, reactor decay ratio and resonance frequency are compared. The first-order model gives correct results, provided that the correct effective fuel time constant is being used, which can be as short as a few seconds.
A benchmark has been performed to compare the performances of exponential autoregressive (ExpAR) ... more A benchmark has been performed to compare the performances of exponential autoregressive (ExpAR) models against linear autoregressive (AR) models with respect to boiling water reactor stability monitoring. The well-known March-Leuba reduced-order model is used to generate the time-series to be analysed, since this model is able to reproduce the most significant non-linear behaviour of boiling water reactors (i.e. converging, diverging and limit-cycle oscillations). In this way the stability characteristics of the signals to be analysed are known a priori. An application to experimental time-traces measured on a thermalhydraulic natural circulation loop is reported as well. All methods perform equally well in determining the stability characteristics of the analysed signals.
The influence of changing the position of the feedwater sparger on the thermal-hydraulic stabilit... more The influence of changing the position of the feedwater sparger on the thermal-hydraulic stability of natural-circulation boiling water reactors (BWRs) is investigated. Frequency-domain, linear stability analysis is applied using a reduced-order dynamic model. It is found that the phase with which the temperature oscillations, created at the feedwater sparger, reach the core inlet has a significant influence on the stability.
A relatively simple subchannel void-fraction measurement system was developed and applied to a sc... more A relatively simple subchannel void-fraction measurement system was developed and applied to a scaled model of a BWR fuel assembly. The measurement system is based upon the gamma-transmission technique and uses a tomographic reconstruction procedure to calculate the void-fractions in the subchannels. Data pre-processing is used to remove positioning errors of the gamma source and detector. Measurements are performed under dierent operating conditions and radial power pro®les. The measurements are compared with the drift-¯ux two-phase¯ow model. The void-fraction in the wall and corner subchannels is lower than average. By applying the drift-¯ux model to each subchannel separately and comparing this calculation with measurements the presence of lateral void-drift should be detectable. However, the data do not show evidence for lateral void-drift. By comparing two chordal void-fractions, one through the fuel rods and one in between the fuel rods, a¯ow pattern transition could clearly be seen between a void-fraction of 30% and 40%. 7
Investigations on Type-I (hydrostatic head) and Type-II (density wave) BWR stability characterist... more Investigations on Type-I (hydrostatic head) and Type-II (density wave) BWR stability characteristics are reported. Experimental data are obtained from the Dodewaard natural-circulation BWR at conditions far away from nominal operating points. The Type-I stability boundary was reached; the Type-II stability boundary was crossed. At this latter unstable condition the reactor power showed peculiar oscillation modulations. Experimentally obtained decay ratios and resonance frequencies are put into context using a physical model. Flashing is shown to be an important phenomenon for driving the coolant flow at start-up conditions and for Type-I stability features. From low-pressure experiments, it appears that the decay ratio is an unsafe measure for Type-II stability close to the stability boundary.
ABSTRACT The evaluation of experimental techniques for the determination of the subcriticality le... more ABSTRACT The evaluation of experimental techniques for the determination of the subcriticality level of an ADS core relies on reactor point kinetics. The measured parameters depend on the detector position, and the reactivity values are subject to spatial correction factors (SCFs). In this paper the contribution of different eigenmodes to the SCF for the pulsed neutron source (PNS) technique is assessed. Moreover by pulse simulations, precise values of the correction factor are obtained. As case study, the VENUS-F SC1 subcritical core is investigated, with a pulsed neutron source in the center of the core, generated by the GENEPI-3C deuteron accelerator. Much more than 100 modes need to be taken into account to precisely obtain the spatial correction factor for the area method evaluation of this core. Especially the modes with a maximum in the center of the core contribute significantly to the SCF. No spatial correction needs to be applied close to the zeros of the first mode with a maximum in the center of the core (different from the fundamental one). In the reflector zone, the absolute reactivity level is overestimated.
The influence of changing the position of the feedwater sparger on the thermal-hydraulic stabilit... more The influence of changing the position of the feedwater sparger on the thermal-hydraulic stability of natural-circulation boiling water reactors (BWRs) is investigated. Frequency-domain, linear stability analysis is applied using a reduced-order dynamic model. It is found that the phase with which the temperature oscillations, created at the feedwater sparger, reach the core inlet has a significant influence on the stability.
From the beginning of BWR technology it was realized that a BWR can become unstable under particu... more From the beginning of BWR technology it was realized that a BWR can become unstable under particular circumstances caused by a feedback between the thermal-hydraulics and the neutronics. This instability can result in oscillations of the power and the flow rate, which is an unwanted phenomenon.The NACUSP project addresses the stability issues in current and future BWRs by expanding the
By altering the coolant flow direction in a pebble bed reactor from axial to radial, the pressure... more By altering the coolant flow direction in a pebble bed reactor from axial to radial, the pressure drop can be reduced tremendously. In this case the coolant flows from the outer reflector through the pebble bed and finally to flow paths in the inner reflector. As a consequence, the fuel temperatures are elevated due to the reduced heat transfer of the coolant. However, the power profile and pebble size in a radially cooled pebble bed reactor can be optimized to achieve lower fuel temperatures than current axially cooled designs, while the low pressure drop can be maintained.
... et al., 2003 WJM De Kruijf, KCJ Ketelaar, G. Avakian, P. Gubernatis, D. Caruge, A. Manera, TH... more ... et al., 2003 WJM De Kruijf, KCJ Ketelaar, G. Avakian, P. Gubernatis, D. Caruge, A. Manera, THJJvan der Hagen, G. Yadigaroglu, G. Dominicus, U. Rohde, H.-M ... Zboray et al., 1999 Zboray, R., Manera, A., De Kruijf, WJM, van der Hagen, THJJ, van Bragt, DDB, van Dam, H., 1999. ...
The use of the decay ratio as a practical stability measure of boiling water reactors is question... more The use of the decay ratio as a practical stability measure of boiling water reactors is questioned. Especially, it is shown that a reactor working at an operating point with a small decay ratio can be closer to instability than a reactor with a larger decay ratio. Consequently, a reconsideration of the practical use of the decay ratio is advocated. :c~
Usually, heat transfer from fuel to coolant is treated as a first-order process in reduced-order ... more Usually, heat transfer from fuel to coolant is treated as a first-order process in reduced-order boiling water reactor dynamic models. The correctness of this simple approach is investigated by comparing reactor stability predictions of the March-Leuba reduced-order model, with those using a second-order model. The predicted margin to instability, reactor decay ratio and resonance frequency are compared. The first-order model gives correct results, provided that the correct effective fuel time constant is being used, which can be as short as a few seconds.
A benchmark has been performed to compare the performances of exponential autoregressive (ExpAR) ... more A benchmark has been performed to compare the performances of exponential autoregressive (ExpAR) models against linear autoregressive (AR) models with respect to boiling water reactor stability monitoring. The well-known March-Leuba reduced-order model is used to generate the time-series to be analysed, since this model is able to reproduce the most significant non-linear behaviour of boiling water reactors (i.e. converging, diverging and limit-cycle oscillations). In this way the stability characteristics of the signals to be analysed are known a priori. An application to experimental time-traces measured on a thermalhydraulic natural circulation loop is reported as well. All methods perform equally well in determining the stability characteristics of the analysed signals.
Uploads
Papers by T.h.j.j. Hagen